Oscillators are used in numerous applications where it is desired to have an alternating current with a stable frequency. However, most oscillation circuits are subject to deviation from their nominal output frequency. These frequency deviations can be due to many sources including temperature variations, which can cause frequency drift, and load variations, which can cause frequency pulling.
In attempts to stabilize these frequency deviations, circuits have been developed which use biasing techniques to eliminate frequency drift and/or additional stages to reduce pulling. However, the biasing techniques tend to load down the resonator of the circuit and de-que its performance. Additional stages add to the overall cost and complexity of the oscillator circuit.
U.S. Pat. No. 5,126,699 describes the use of a temperature sensor whose reading is used by a temperature compensation algorithm within a microprocessor to determine what DC value should be added to modulation to maintain a desired oscillator frequency. Clearly, a temperature sensor and a microprocessor adds significant cost.
In view of the above, there is a need for an oscillator circuit that compensates for frequency drift and frequency pulling due to temperature variations and load variations, respectively, without adding significant cost or complexity to the circuit.